After upgrading to ITMS 8.5 RU4 some plug-ins on a few machines are not being updated and the policy fails with exit code 1619 in the agent.log files.
ITMS 8.5 RU4
Environment had been upgraded from 7.5 to 7.6 to 8.1 to 8.5 RU4 between 2015 and 2022.
Custom policies had been cloned from the out-of-box plug-in install and update policies which resulted in duplicate copies of plug-in update packages.
NOTE: The root cause of the exit code 1619 was that an old reference to an old package pointed to an old command-line that used a 7.x update installer that no longer existed.
Identified the problem package GUIDs and package names using the Software Delivery folder, the SMP Console, and the FIND GUID query.
From the SMP Console, found the duplicate packages and deleted all but the most recent in the following location:
Manage > All Resources > Package > Software Package
Then went to the Resource Membership Update in the SMP Console and ran the Delta & Policy update schedules.
Then did an Update Configuration on the Package Server(s).
Then did an Update Configuration on the affected Symantec Agent machines.